抄録
Glycine is a major inhibitory neurotransmitter in the spinal cord and brain stem. Glycine acts by increasing the Cl- permeability through activation of a specific receptor/ion channel complex consisting of a pentameric subunit assembly. Molecular cloning has disclosed the nature of receptor subunits α and β. While the role of the β subunit is still unclear, the α subunit functions in both ligand (agonist/antagonist) binding and ion channel formation. It has been demonstrated that there are two isoforms of the α subunit, α1 and α2. The mRNAs encoding these subunit isomers are transcribed from different genes, in spite of their structural similarity. The α1 mRNA is abundant in adult spinal cord, whereas the α2 mRNA is mainly expressed in developing spinal cord as well as various regions of brain tissue. The single channel properties were examined in outside-out patches excised from Xenopus oocyte membrane expressing α1 or α2 homomeric receptors. The mean open time of α2 channels was 70-times longer than that of α1 channels. The subunit switching from α2 to α1, and resulting shortening of channel kinetics, may ensure a rapid motor control in adult animals.
